Streptococcus equi ssp zooepidemicus and canine respiratory disease

Josepha DeLay, Emily Brouwer, Đurđa Slavić, Margaret Stalker

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2021;25(4):24.

The bodies of 2 young adult female mixed breed dogs were submitted to the Animal Health Laboratory for postmortem examination.  Both dogs originated from multi-dog housing where outbreaks of respiratory disease had recently occurred.  Dog A deteriorated rapidly and died while being treated.  Dog B developed pneumothorax and was euthanized. 

Lung from dog A had diffuse dark red discoloration and mild rubbery consistency.  Lung lesions in dog B included diffuse atelectasis, as well as unilateral (right) red-tan discoloration, firm texture (consolidation), and pleural adhesions (Fig. 1).  Histologically in lung from both dogs, bronchiolar lumens and alveoli were filled with aggregates of neutrophils variably mixed with macrophages and fibrin.  Fibrin thrombi were present in either alveolar capillaries or larger pulmonary blood vessels.  In dog B, additional lung lesions included patchy alveolar hemorrhage and necrosis, and pleural and alveolar septal fibrosis.   Numerous coccobacilli were present among alveolar inflammatory cells in dog A.

Figure 1. Lung is firmly and focally adherent to parietal pleura (arrow), and there is multifocal consolidation (asterisk) in lung parenchyma.

The inflammatory lesions in lung from each dog were typical of a bacterial etiology, and Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) was isolated in moderate to large number from lung of both animals.  PCR tests for various viral pathogens (canine parainfluenza virus, canine adenovirus 2, canid herpesvirus-1, canine distemper virus, influenza A virus) identified concurrent, low level infection with canine parainfluenza virus in dog 1, but did not detect any of these viruses in lung from dog 2. 

S. zooepidemicus is recognized as a contributor to the canine infectious respiratory disease (CIRD) complex (‘kennel cough’), and may be the main pathogen identified in respiratory disease outbreaks in kennels and shelters.  Rapid progression of pneumonic clinical signs and a poor prognosis have been described in dogs with respiratory disease attributed to S. zooepidemicus.  Typical lesions are similar to those present in the dogs in this report, including fibrinosuppurative and necrotizing or hemorrhagic bronchopneumonia, sometimes with pleuritis. 

Although more frequently encountered as an opportunistic pathogen in horses, S. zooepidemicus has also been isolated from other species in addition to canids.  Recent outbreaks of S. zooepidemicus in swine have been associated with a highly pathogenic strain containing specific SzM gene mutations which were not detected in either canine isolate evaluated in this case report.   AHL

References

1. Day MJ, et al. Aetiology of canine infectious respiratory disease complex and prevalence of its pathogens in Europe.  J Comp Path 2020;176:86-108.

2. Preistnall SL, et al. New and emerging pathogens in canine infectious respiratory disease.  Vet Pathol 2014;51(2):491-504.

3. Velineni S, et al. Clones of Streptococcus zooepidemicus from outbreaks of hemorrhagic canine pneumonia and associated immune responses. Clin Vaccine Immunol 2014;21(9):1246-1252.